Donald Trump at the opening of Trump Turnberry in Ayrshire last summer.
Photograph: Murdo Macleod for the Guardian

Donald Trump has resigned as a director of his four Scottish golf and tourism firms, raising fresh questions about the US president’s business interests.

Filings at Companies House, the UK government agency that holds and publishes documents on all British businesses, show Trump resigned as a director of the four companies on 19 January, the day before his inauguration.

However, no filings show any change to Trump’s ultimate ownership of the businesses, which centre on his two golf resorts in Aberdeenshire and Ayrshire and have an estimated investment value of more than £180m.

According to the documents, the president has resigned as a director for Trump International Golf Club Scotland, which owns the course and boutique hotel that Trump opened north of Aberdeen in 2012.

He has also resigned as director of two firms which own the Trump Turnberry resort in Ayrshire – SLC Turnberry and its parent company Golf Recreation Scotland.

The fourth company is DT Connect Europe, which owns the Sikorsky helicopter that Trump brought from Florida in 2014 to transport his family between their two Scottish courses and to service wealthy golfers flying in to Prestwick airport, north of Turnberry.

Trump pledged earlier in January to resign directorships in all his companies in an effort to satisfy intense criticism from White House ethics experts about the risks of conflicts of interest between his business interests and his presidency.

Trump said day-to-day control of the Trump Organisation’s businesses would pass to his sons Eric and Donald Jr and a company executive, Allen Weisselberg, who would run them in a trust.

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The change in directorships appears to leave Eric Trump as the most dominant family member in Scotland. He is now the sole director of Golf Recreation Scotland, which has Trump Turnberry as its registered business address.

But Democrat and Republican ethics experts have been scathing about Trump’s divestment strategy since he has failed to sell his shares and holdings, nor has he put them in a blind trust, which means he will continue to be a direct beneficiary of their profits or future sale.

Company records seen for Trump International Golf Club Scotland in Aberdeenshire, the loss-making course into which the president has sunk £40m, show that 999 of its 1,000 shares were held directly by Trump in September 2015 – the most recent filing detailing the business’s share ownership.

The latest company report discloses that the resort can only survive with Trump’s money. The club’s executives said the resort’s expansion plans, potentially including a major new private housing estate, were not affected by Trump’s pledge to drop all new or pending overseas investments, since they were simply “future phasing” of an existing property.

Executives at Turnberry, home to one of the UK’s most famous Open golf venues and a five-star hotel Trump bought for £34m in 2014, say the business has been booming since Trump ploughed more than £100m in the course’s overhaul and the hotel’s refurbishment.

After years recording heavy losses, a Turnberry executive told the Guardian this month the business was on course to make the largest profit in its 100-year history.

Its prosperity had been buoyed by the soaring value of the US dollar against the pound after the UK vote to leave the EU resulted in a sharp fall in sterling’s value, boosting visits by American golfers.

Andy Wightman, a Scottish Green party MSP and land ownership expert who has studied Trump’s Aberdeenshire business, said there were clear risks of a conflict of interest for Trump, particularly during the negotiations over a future US-UK trade deal.

“It is clear that by retaining ownership of 99.9% of Trump International Golf Club Scotland, President Trump is in ultimate control of this company and his efforts to secure a trade deal with the UK are compromised by his continued business interests in the UK,” Wightman said.

Trump’s ownership of the companies is complex, leading in Turnberry’s case to the US state of Delaware, which has very loose company reporting regulations but offers substantial tax advantages. Other than the president’s resignation as director, Companies House filings show no recent change in their UK ownership or shareholdings.

The latest accounts for SLC Turnberry say its parent company is Golf Recreation Scotland, whose “parent undertaking” is the Donald J Trump Revocable Trust, which is registered in New York. It adds that “the ultimate controlling party is Mr Donald J Trump”.

However, the latest annual return for Golf Recreation Scotland shows that as of February 2016, its 1m shares are held by a Delaware-registered limited liability company called Turnberry Scotland LLC.

A Wall Street Journal investigation in December found that at least half – roughly $304m – of the revenues Trump declared in his federal financial disclosure were held in 96 LLCs registered in Delaware.

Those included his famous residence and club at Mar-a-Lago in Palm Beach, Florida, and his skyscraper at 40 Wall Street in New York, a fairground carousel that operates in Central Park, New York, as well as the Sikorsky helicopter based in the UK.

The shareholdings in many of these companies were interlinked; the WSJ said the opacity and complexity of Trump’s myriad holdings made it far harder to gauge the full extent of any potential conflicts of interest the president would face.